Revealing the secrets of an earthquake: physico-chemical constraints from a multidisciplinary study of exhumed faults

Understanding the physico-chemical processes controlling faulting and earthquake generation is essential in seismic hazard assessment. Since dreadful earthquakes nucleate at depth (10-15 km), direct access to seismic sources is impossible and monitoring active faults from the Earth surface, or interpreting radiated seismic waves, yield limited information on earthquake mechanics. The indirect analysis of earthquakes is unable to provide tight constraints on fundamental mechanical parameters such as the dynamic fault strength and the energy budget of an earthquake. Here we propose (i) to investigate earthquake processes by studying fossil seismic sources (e.g., faults containing solidified melts produced during seismic slip or pseudotachylytes) now exhumed at the Earth's surface and (ii) to analyze the fault rock materials in the laboratory by a novel multidisciplinary approach involving the up-to-date techniques in microstructural analysis, mineralogy and petrology. In parallel with the study of natural faults we will develop a new apparatus to perform experiments under the extreme deformation conditions typical of earthquakes (e.g., slip velocities of ~ 1 m/s) simulating seismic slip in the lab. There is only one apparatus of this kind, located in Kyoto-Japan, currently operating in the world. Collaboration with the Kyoto University will serve to design the new high friction apparatus to be built in Padova. The experiments in Kyoto will be complemented by experiments at Brown University (RH, USA) with a high-pressure apparatus to investigate the mechanical behavoiur of different fault rocks including fault gouges. Field work will investigate exceptional exposures of faults in Europe and Australia. The study of natural faults will proceed together with theoretical modeling calibrated on the basis of the field data, the mechanical data from rock-friction experiments and the analytical data of natural and experimental deformation products. The integration of all data is expected to yield estimates of seismic source parameters (e.g., dynamic shear stress, the seismic energy budget, all challenging issues for Earth scientists) and to provide an insight into the mechanisms of earthquake nucleation. The proposed study has implication also in the understanding of other friction-controlled processes important in Earth Sciences (e.g., rock landslides) as well as in industry. It is noteworthy that the experimental results will find application to improve industrial milling techniques. The development of the new dedicated laboratory will allow Padova University to compete at top scientific level with the world’s leading institutions for the study of earthquake mechanics.